Nuclear medicine is a unique medical specialty wherein radiation is used to acquire images which show the function and anatomy of organs, bones or tissues of the body. Radiopharmaceuticals are introduced into the body, either by injection or ingestion, and are attracted to specific organs, bones or tissues of interest. Such radiopharmaceuticals produce gamma photon emissions which emanate from the body. One or more detectors are used to detect the emitted gamma photons, and the information collected from the detectors is processed to calculate the position of origin of the emitted photon from the source (i.e., the body organ or tissue under study). The accumulation of a large number of detected gamma positions allows an image of the organ or tissue under study to be displayed.
In certain nuclear tomographic imaging techniques, such as Single Photon Emission Computed Tomography (SPECT), events are detected by one or more collimated radiation detectors, also referred to as gamma cameras, which are typically rotated about a patient's body in a defined orbital path. The collimators employed with such detectors have apertures running through the body of the collimator to assure that only gamma photons traveling along specific paths aligned with the holes will pass through to the detector. Upon detection of a gamma ray, it is inferred that the gamma ray then came along the same path that the collimator hole is directed.
Collimator design conventionally is non-adaptive, meaning that the design of the collimator with respect to length, septa, dimensions and focal or parallel nature of the collimator holes cannot be adjusted. Therefore, if different resolution and sensitivity is desired, the collimator needs to be replaced with another collimator having different dimensions and focal characteristics. For example, in some imaging applications a single or multi-focal collimator should be used, while in other applications a parallel hole collimator should be used. Each different design of collimator may have a different optimal region or so-called “sweet spot” within its FOV in which the ROI of an imaged object should remain for optimal results.
FIG. 1 illustrates one example of a prior art focusing collimator. The focusing collimator 2 contains a number of channels 4 separated by septa 10. The channels 4 are all aimed at a common focal point 6. The collimator thus receives a “fan beam” 8 of radiation emitted from focal point 6. Consequently, it is desirable in imaging applications using such a focusing collimator to maintain the ROI centered at focal point 6 in the FOV of the collimator.
In SPECT as well as planar imaging, image scanning consists of multiple image data acquisitions taken over multiple planar view angles with respect to the patient. Frequently, the target organ (e.g., the heart) or the ROI has to be positioned with respect to the detector head so that it remains within an optimal collimation area within the FOV of the detector, which varies depending on the design of the collimator (e.g. whether the collimator is a focusing collimator, multi-focal collimator, parallel hole collimator, etc.).
FIG. 2 illustrates a typical scenario with respect to a target organ 201, a FOV 202, and a “sweet spot” or optimal imaging area 203 within the FOV 202. Conventionally, the initial detector head positioning is done manually by a technician based on only a few views. Thus, for example, for view angle 1, the target organ is optimally positioned within the sweet spot 203 of the collimator FOV 202; however for view angle N, which corresponds to a position of the detector head that is rotated with respect to the initial position of the detector head for view angle 1, the target organ 201 is outside the sweet spot 203 (while continuing to be within the overall FOV 202). In this case, sub-optimal image data will be acquired from view angle N. To avoid this result, it would be necessary for the technician to make manual adjustments at each different view angle, which would be time consuming and not necessarily consistent from view to view. Accordingly, there exists a need for improvement in the art with respect to maintaining a target organ or ROI within an optimal imaging area of a FOV of a detector head over all view angles.